1. Field of the Invention
Embodiments of the invention relate to the field of plasma generation. More particularly, the present invention relates to a system and method for selectively controlling the density, temperature, and composition of ions and radicals and the density and energy of electrons in sub-atmospheric pressure plasmas.
2. Discussion of Related Art
Plasmas are used in a variety of ways in semiconductor processing, such as plasma enhanced chemical vapor deposition (PECVD), and substrate doping. Such processes involve the directional deposition or doping of ions on or beneath the surface of a targeted substrate, such as silicon wafers. Other processes include plasma etching, where the directionality of the etching species determines the quality of the trenches to be etched.
Typical plasma doping processes exploit the charged nature of ions within the plasma to deposit the ions on or beneath a targeted surface while plasma deposition processes rely on neutrals to deposit on the surface of the substrate. Because neutrals are not charged, they can be difficult to control and can, therefore, build up on surfaces in a manner which hinders final processing.
In addition, plasmas typically contain different ion and neutral species. To perform a particular process it would be desirable to maximize a particular species and to minimize another species within the plasma. It would also be advantageous to have a method for providing greater control over the composition of the plasma as compared to current methods.
Thus, there is a need for a method for controlling the ion composition and density of a plasma to maximize the presence of desired ion species, and to minimize the presence of undesired ion species and neutrals for doping applications. For other applications, such as etching and deposition, the reverse may be preferred where neutrals are preferred.